This study explored how mental illness shapes transitions to marriage among unwed mothers using augmented data from the Fragile Families and Child Wellbeing study. We estimated proportional hazard models to assess the effects of mental illness on the likelihood of marriage over a five year period following a non-marital birth. History of diagnosed mental illness was obtained from the survey respondents’ prenatal medical records. We found that mothers with diagnosed mental illness were about two thirds as likely to marry as mothers without mental illness, even after controlling for demographic characteristics, and that the association is explained little by measures of human capital, relationship stability, partner selection, cognitive ability, and substance use. (Author abstract)